This study aims at describing the role of lysosomes in regulating collagen production in fibroblasts. The regulation of collagen has clear health-related implications because of the number of human diseases that are associated with a change in collagen metabolism. Acquired disorders such as rheumatoid arthritis, pulmonary fibrosis, cirrhosis, and atherosclerosis, involve significant changes in collagen content and type in affected tissues. The genetic disorders such as the Ehlers Danlos syndromes and Osteogenesis Imperfecta demonstrate various aspects of deficiencies in collagen regulation. Based on recent data from several laboratories that intracellular degradation of newly synthesized collagen is widespread in fibroblasts and that it can in part be inhibited by lysosomal inhibitors, a role for lysosomes in collagen biosynthesis has been implicated. One role of lysosomes has been shown to involve the degradation, intracellularly, of a portion of newly synthesized, structurally defective, collagen. A second role for lysosomes to be tested here is their hypothesized involvement in the translational regulation of collagen synthesis and its secretion. The role of lysosomes is, however, complicated by the presence of at least one non-lysosomal pathway for the basal levels of intracellular degradation of newly synthesized collagen. The first aim of the present proposal is to use cultured chick tendon fibroblasts to determine if procollagen or procollagen fragments are found in lysosomes. The second aim is to examine cultured fibroblasts which are inhibited in theri ability to secrete procollagen to determine if decreased secretion also results in decreased translation, and if this decreased translation is a result of regulation of procollagen production involving lysosomes. The third aim is to determine whether lysosomes may be involved in the uptake of either procollagen or procollagen extension propeptides either alone or by a receptor-mediated process. In order to characterize further intracellular degradation in cultured fibroblasts, the fourth aim is to examine the basal level of degradation to determine if oxygen-derived free radicals and/or neutral proteases are responsible for this important non-lysosomal pathway.